1. Field of the Invention
The present invention relates to golf balls. Specifically, the present invention relates to golf balls that include a core, a mid layer, a cover and dimples.
2. Description of the Related Art
Golf balls have a large number of dimples on the surfaces thereof. The dimples disturb the air flow around the golf ball during flight to cause turbulent flow separation. This phenomenon is referred to as “turbulization”. Due to the turbulization, separation points of the air from the golf ball shift backwards leading to a reduction of drag. The turbulization promotes the displacement between the separation point on the upper side and the separation point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. Excellent dimples efficiently disturb the air flow. The excellent dimples produce a long flight distance.
There have been various proposals for dimples. US2007/0149321 (JP2007-175267) discloses a dimple pattern in which the number of units present in a high-latitude region is different from the number of units present in a low-latitude region. US2007/0173354 (JP2007-195591) discloses a dimple pattern in which the number of types of dimples present in a low-latitude region is greater than the number of types of dimples present in a high-latitude region. US2013/0196791 (JP2013-153966) discloses a dimple pattern in which the density of dimples is high and variations in sizes of dimples are small. US2009/0191982 (JP2009-172192) discloses a golf ball that has randomly arranged dimples. The dimple pattern of the golf ball is referred to as a random pattern. US2012/0004053 (JP2012-10822) also discloses a golf ball having a random pattern.
Golf players require not only flight performance but also controllability for golf balls. A proposal for achieving both flight performance and controllability was made in JP2010-188199. A similar proposal was also made in JP2013-31778.
If a golf ball is hit with an iron, an excessive lift force is generated. The lift force may cause rising of the golf ball during flight. The rising is the cause of variations in flight distances. The golf ball is inferior in stability of flight distance. It is not easy for golf players to let the golf ball land on a target point.
An objective of the present invention is to provide a golf ball that is excellent in flight performance in a shot with a driver, flight distance stability in a shot with an iron, and controllability in an approach shot.